Thermal Spray of Repair and Protective Coatings

ABSTRACT

This invention provides a method for graphene or graphene oxide reinforcement in a metallic thermal spray coating. The incredible properties of graphene and graphene oxide make them attractive options to increase the mechanical properties in a variety of materials. Recent developments in the manufacturing of graphene oxide and reduced graphene oxide powders have greatly reduced their cost, making them viable additives in thermal spray powders for widespread use in industry.

TECHNICAL FIELD OF THE INVENTION

The present invention relates in general to the field of graphite, and more particularly, to compositions and methods of thermal spray of repair and protective coatings.

BACKGROUND OF THE INVENTION

Without limiting the scope of the invention, its background is described in connection with composite materials.

Thermal Spray Coating Technology: Plasma spray is one of the most versatile forms of a thermal spray process. Plasma is capable of spraying all materials that are considered spray able.

In plasma spray devices, an arc is formed in between two electrodes in a plasma forming gas, which usually consists of either argon/hydrogen or argon/helium. As the plasma gas is heated by the arc, it expands and is accelerated through a shaped nozzle, creating velocities up to MACH 2. Temperatures in the arc zone can approach 36,000° F. (19,982° C.). Temperatures in the plasma jet can still be 18,000° F. (9,982° C.) several centimeters from the exit of the nozzle. Powders may be injected after the plasma. This technique is sometimes referred to as remote plasma deposition. It relies on placing the powder in the jet stream where gas is no longer ionized but is a highly energetic species.

In the cold spray coating technique, powder particles are accelerated to supersonic velocities (600-1500 m/s) by a carrier gas flowing under large pressure difference (up to 3.5 MPa) through a de Laval type of nozzle and made to impact onto a substrate. Cold spraying has unique advantages, such as: minimal effects on the material sprayed, like oxidation, grain coarsening or phase changes, produces highly dense coatings, and substrate is not affected during the coating process.

The disadvantages of a cold spray process are that a large amount of carrier gas is lost, unless recycled, and that only plastically deformable materials can be deposited.

In a cold spray process there is no melting of the particles and bonding is believed to be due to adiabatic shear instabilities arising from thermal softening at the particle/substrate and particle/particle interface. Cold spraying has been used to deposit many types of materials including pure metals, alloys and composite materials. In all of these cases of spraying a composite coating, it was observed that the second phase was distributed uniformly within the matrix. It has been the desire of researchers to spray composites containing nanofillers as reinforcements using a cold or plasma spraying technology.

In previous research, cold plasma spraying was used to deposit a blend of aluminum powder that was an agglomeration of powders comprising aluminum-silicon and CNTs. The powder feeder used was a Praxair 1264HP. The powder feeder has a maximum pressure capability of 3.4 MPa. The main gas pressure was kept at a pressure of 2.9 MPa with the use of an additional Argon or Nitrogen carrier gas for the powder delivery. The carrier gas was kept 0.1 MPa to facilitate the injection of the powder into the jet. The nozzle was fixed to a frame and the substrate was fixed onto an X-Y traverse table, the movement of which was programmable by using a computer. Eight layers were sprayed to build up the coating thickness on a 6061 aluminum alloy substrate resulting in improved strength and enhanced corrosion protection.

Thermal spray coatings have numerous inherent defects. The coatings lack bulk strength. Development of residual stress lowers the adhesion strength at high thicknesses. High temperatures during deposition create unwanted oxides. The addition of the graphene or graphene oxide has proven to increase cohesion and adhesion strength at large thicknesses in the model composition, Nickel-5% Aluminum. It has also proven to reduce unwanted (metallic) oxide content within the coatings.

There are hundreds of commercially available thermal spray powders. Many of those powder compositions are approved by the OEM for specific repairs on jet engine components. Many of these specific repairs would benefit from increased strength and wear properties.

SUMMARY OF THE INVENTION

Plasma spray deposition technology is one that directly translates to large area applications. Carbon nanotubes can be deposited using a plasma spray process to enhance mechanical strength and corrosion protection. This process used carbon nanotubes placed in a polymer suspension. The suspension was then aerosolized in a spray dryer to form micron-scale polymer carbon nanotube composite particles. The composite particles are injected past the peak energy portion of the plasma where the energetic kinetic of the plasma both evaporates the polymer host and accelerates the superheated carbon nanotubes to supersonic speeds prior to impact on the surface of a substrate. The plasma itself also bathes the surface of the substrate with energetic monotonically decaying ionized particles. The combination of energy from the accelerated carbon nanotubes and monotonically decaying ionized particles is sufficient to achieve bind both to the surface of the substrate and the carbon nanotubes and between the nanotubes (both in and out of the plane of the deposition).

A Graphene or graphene oxide (G/GO) reinforced composite was achieved using thermal spray. There are two delivery methods to inject the graphene or graphene oxide into the plasma spray system. The first method uses dry mixing all of the components of the composite material in a mill to form a homogenous dispersion of all of the elements in the powder. The powder is then injected just beyond the plasma into what is referred to as the flame section into the plasma stream. The plasma stream both heats the powder and accelerates it to high velocities. The combination of heated particles traveling at high velocities allows the powders to be deposited on a substrate forming a composite coating. The second approach is to suspend the G/GO in a solvent at a concentration that allows the suspension to be aerosolized and injected into a cooler portion of the plasma gas stream. In both cases the use of an inert gas shroud eliminates the super-heated powder from either burning the G/GO in the presence of oxygen and prevents the formation of an unwanted metal oxide phase in the deposited composite.

The coatings created by this invention have higher strength and better wear properties than coatings created using only the stock Ni-185 powder. The simple modification of the powder composition increased the mechanical properties of the resulting coatings. Modifying the conventional thermal spray configurations with either the inert shroud or the solution suspension further increases these properties and maximizes the retention of the additive within the coatings.

In one embodiment, the present invention includes a method of depositing a composite on a surface comprising: providing a surface; providing graphene/graphene oxide flakes; providing metal and/or metal oxide powder; and thermally spraying the graphene/graphene oxide flakes together with the metal and/or metal oxide material on said surface, whereby the resulting composite has enhance mechanical and corrosion resistant properties. In one aspect, the graphene/graphene oxide flakes and the metal and/or metal oxide material are dry mixed together prior to spraying. In another aspect, the metal and/or metal oxide powder is Ni/Al₂O₃ powder. In another aspect, the graphene/graphene oxide flakes are introduced as an atomization of a suspension separately from the metallic powder. In another aspect, the graphene/graphene oxide flakes are suspended in water or another polar solvent. In another aspect, the concentration of the graphene/graphene oxide flakes suspension is from 0.1% and 0.5% wt. In another aspect, the graphene has an oxidation level >1% wt. In another aspect, the graphene/graphene oxide flakes are suspended in ethanol or another non-polar solvent. In another aspect, the concentration of the graphene/graphene oxide flakes suspension is from 0.1% and 0.5% wt. In another aspect, the graphene has an oxidation level >1% wt.

In another embodiment, the present invention includes a method of depositing a composite on a surface comprising: providing a surface; providing crystalline graphene/graphene oxide flakes suspended in water or another polar solvent; providing metal and/or metal oxide powder; and thermally spraying the crystalline graphene/graphene oxide flakes together with the metal and/or metal oxide material on said surface, whereby the resulting composite has enhance mechanical and corrosion resistant properties. In one aspect, the crystalline graphene/graphene oxide flakes and the metal and/or metal oxide material are dry mixed together prior to spraying. In another aspect, the metal and/or metal oxide powder is Ni/Al₂O₃ powder. In another aspect, the crystalline graphene/graphene oxide flakes are introduced as an atomization of a suspension separately from the metallic powder. In another aspect, the crystalline graphene/graphene oxide flakes are suspended in water are from 0.1% to 0.5% wt to volume. In another aspect, the concentration of the crystalline graphene/graphene oxide flakes suspension is from 0.1% to 0.5% wt to volume in a polar solvent. In another aspect, the crystalline graphene/graphene oxide flakes has an oxidation level >1% wt. In another aspect, the graphene flakes are suspended in ethanol or another non-polar solvent. In another aspect, the concentration of the crystalline graphene/graphene oxide flakes suspension is from 0.1% to 0.5% wt. In another aspect, the graphene has an oxidation level >1% wt.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures and in which:

FIG. 1 shows a TEM, which shows coatings having a very high efficiency of G/GO retention;

FIG. 2 is a SEM showing other enhanced properties; and

FIG. 3 shows a tafel plot of the plasma spray composite material.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention.

To facilitate the understanding of this invention, a number of terms are defined below. Terms defined herein have meanings as commonly understood by a person of ordinary skill in the areas relevant to the present invention. Terms such as “a”, “an” and “the” are not intended to refer to only a singular entity, but include the general class of which a specific example may be used for illustration. The terminology herein is used to describe specific embodiments of the invention, but their usage does not delimit the invention, except as outlined in the claims.

A powder that includes the components of the composite were mixed in a plastic container using a horizontal jar mill, a speed from 20 RPM to 1000 RPM preferably 100 RPM, for between 2 and 10 hours but at least 6 hours continuously. The powder constituents include 10:1 ratio of Nickel to Alumina powder and a small amount (0.05%-4.0% wt) of the graphene and/or graphene oxide. In one example, the graphene and/or graphene oxide is a crystalline graphene and/or graphene oxide. The combined powder (G/GO/Al₂O₃) is injected into the gas stream beyond the plasma. This region is often referred to as the plasma's flame and consists of a combination of ionized species and highly energetic molecules. An inert, argon gas shroud is used to prevent oxidizing or burning of the G/GO. G/GO can oxidize or burn at temperatures greater than 400° C. in the presence of oxygen and prevent the formation of an unwanted metal (nickel) oxide. The insertion of the G/GO/Al₂O₃ powder occurs in a region ranging from 0.5 mm to 20 mm down stream from the plasma. The insertion of powder creates a small amount of turbulence in the gas stream inducing additional mixing of the powders. This produces a coating with a uniform distribution of G/GO through out the Ni/Al₂O₃ deposition. The GO/Ni/Al₂O₃ composite coating has improved microstructure, decreased unwanted (metallic) oxide phases, enhanced mechanical properties, and ware resistance properties.

Alternatively, G/GO can be introduced into the composite through an atomization of a suspension of the G/GO material separately from the metallic powder. The G/GO flakes can be suspended in a solution and sonicated to achieve a uniform dispersion. The GO suspension solution is water or another polar solvent where the GO has an oxidation level >1% wt. The GO suspension solution is ethanol or another non-polar solvent where the GO has and oxidation level <1% wt. The concentration of the G/GO suspension was demonstrated from 0.1% and 0.5% wt. Concentrations greater than 1% wt are too viscous to be easily aerosolized. The aerosolized droplets are injected into the gas stream at a flow rate between 5 mL/min and 200 mL/min but nominally at flow rates 40 mL/min and 90 mL/min. The aerosolized droplets are injected into the non-ionized gas stream of the plasma spray system in a region that has sufficient energy to vaporize the liquid but not burn or other wise damage the G/GO additive. The G/GO droplet insertion point occurs in a region ranging from 0.5 mm to 40 mm downstream from the plasma plume. The Ni/Al₂O₃ powder is inserted to the hottest section of the plasma plume or flame using the conventional method to ensure uniform melting. The insertion of Ni/Al₂O₃ powder and G/GO droplets create a small amount of turbulence in the gas stream inducing additional mixing inflight and are deposited simultaneously. The plasma flame/plume is enclosed in an inert gas shroud to prevent the formation of unwanted metal oxides and reduce the combustion of G/GO in air.

The resulting coatings were observed to have a very high efficiency of G/GO retention; this can be seen in TEM (See FIG. 1). Results of another analytical technique, SEM, can be seen in FIG. 2. The deposited composite material had improved microstructure, enhanced mechanical properties and improved corrosion resistance to seawater relative to Ni/Al₂O₃ and other materials. FIG. 3 shows a tafel plot of the plasma spray composite material.

Therefore, in the present invention a Graphene or graphene oxide (G/GO) reinforced composite was achieved using thermal spray. Two delivery methods were used to inject the graphene or graphene oxide into the plasma spray system. The first method used dry mixing all of the components of the composite material in a mill to form a homogenous dispersion of all of the elements in the powder. The powder is then injected just beyond the plasma, e.g., into an area of the plasma that is referred to as the flame section, into the plasma stream. The plasma stream both heats the powder and accelerates it to high velocities. The combination of heated particles traveling at high velocities allows the powders to be deposited on a substrate forming a composite coating. The second method used suspends the G/GO in a solvent at a concentration that allows the suspension to be aerosolized and injected into a cooler portion of the plasma gas stream. In both cases an inert gas can be added as a shroud that eliminates the super-heated powder from either burning the G/GO in the presence of oxygen and prevents the formation of an unwanted metal oxide phase in the deposited composite.

It was found that the coatings created by this invention have higher strength and better wear properties than coatings created using only the stock Ni-185 powder. The modification of the powder composition increased the mechanical properties of the resulting coatings. Modifying the conventional thermal spray configurations with either the inert shroud or the solution suspension further increases these properties and maximizes the retention of the additive within the coatings.

Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

It is contemplated that any embodiment discussed in this specification can be implemented with respect to any method, kit, reagent, or composition of the invention, and vice versa. Furthermore, compositions of the invention can be used to achieve methods of the invention.

It will be understood that particular embodiments described herein are shown by way of illustration and not as limitations of the invention. The principal features of this invention can be employed in various embodiments without departing from the scope of the invention. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, numerous equivalents to the specific procedures described herein. Such equivalents are considered to be within the scope of this invention and are covered by the claims.

All publications and patent applications mentioned in the specification are indicative of the level of skill of those skilled in the art to which this invention pertains. All publications and patent applications are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.

The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and/or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.” The use of the term “or” in the claims is used to mean “and/or” unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and/or.” Throughout this application, the term “about” is used to indicate that a value includes the inherent variation of error for the device, the method being employed to determine the value, or the variation that exists among the study subjects.

As used in this specification and claim(s), the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps. In embodiments of any of the compositions and methods provided herein, “comprising” may be replaced with “consisting essentially of” or “consisting of”. As used herein, the phrase “consisting essentially of” requires the specified integer(s) or steps as well as those that do not materially affect the character or function of the claimed invention. As used herein, the term “consisting” is used to indicate the presence of the recited integer (e.g., a feature, an element, a characteristic, a property, a method/process step or a limitation) or group of integers (e.g., feature(s), element(s), characteristic(s), propertie(s), method/process steps or limitation(s)) only.

The term “or combinations thereof” as used herein refers to all permutations and combinations of the listed items preceding the term. For example, “A, B, C, or combinations thereof” is intended to include at least one of: A, B, C, AB, AC, BC, or ABC, and if order is important in a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB. Continuing with this example, expressly included are combinations that contain repeats of one or more item or term, such as BB, AAA, AB, BBC, AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan will understand that typically there is no limit on the number of items or terms in any combination, unless otherwise apparent from the context.

As used herein, words of approximation such as, without limitation, “about”, “substantial” or “substantially” refers to a condition that when so modified is understood to not necessarily be absolute or perfect but would be considered close enough to those of ordinary skill in the art to warrant designating the condition as being present. The extent to which the description may vary will depend on how great a change can be instituted and still have one of ordinary skilled in the art recognize the modified feature as still having the required characteristics and capabilities of the unmodified feature. In general, but subject to the preceding discussion, a numerical value herein that is modified by a word of approximation such as “about” may vary from the stated value by at least ±1, 2, 3, 4, 5, 6, 7, 10, 12 or 15%.

Additionally, the section headings herein are provided for consistency with the suggestions under 37 CFR 1.77 or otherwise to provide organizational cues. These headings shall not limit or characterize the invention(s) set out in any claims that may issue from this disclosure. Specifically and by way of example, although the headings refer to a “Field of Invention,” such claims should not be limited by the language under this heading to describe the so-called technical field. Further, a description of technology in the “Background of the Invention” section is not to be construed as an admission that technology is prior art to any invention(s) in this disclosure. Neither is the “Summary” to be considered a characterization of the invention(s) set forth in issued claims. Furthermore, any reference in this disclosure to “invention” in the singular should not be used to argue that there is only a single point of novelty in this disclosure. Multiple inventions may be set forth according to the limitations of the multiple claims issuing from this disclosure, and such claims accordingly define the invention(s), and their equivalents, that are protected thereby. In all instances, the scope of such claims shall be considered on their own merits in light of this disclosure, but should not be constrained by the headings set forth herein.

All of the compositions and/or methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions and/or methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims. 

What is claimed is:
 1. A method of depositing a composite on a surface comprising: providing a surface; providing graphene/graphene oxide flakes; providing metal and/or metal oxide powder; and thermally spraying the graphene/graphene oxide flakes together with the metal and/or metal oxide material on the surface, whereby the resulting composite has enhance mechanical and corrosion resistant properties.
 2. The method of claim 1, wherein the graphene/graphene oxide flakes and the metal and/or metal oxide material are dry mixed together prior to spraying.
 3. The method of claim 1, wherein the metal and/or metal oxide powder is Ni/Al₂O₃ powder.
 4. The method of claim 1, wherein the graphene/graphene oxide flakes are introduced as an atomization of a suspension separately from the metallic powder.
 5. The method of claim 4, wherein the graphene/graphene oxide flakes are suspended in water or another polar solvent.
 6. The method of claim 5, wherein the concentration of the graphene/graphene oxide flakes suspension is from 0.1% and 0.5% wt.
 7. The method of claim 6, wherein the graphene/graphene oxide flakes has an oxidation level >1% wt.
 8. The method of claim 4, wherein the graphene/graphene oxide flakes are suspended in ethanol or another non-polar solvent.
 9. The method of claim 8, wherein the concentration of the graphene/graphene oxide flakes suspension is from 0.1% and 0.5% wt.
 10. The method of claim 8, wherein the graphene/graphene oxide flakes has an oxidation level >1% wt.
 11. A method of depositing a composite on a surface comprising: providing a surface; providing crystalline graphene oxide flakes suspended in water or another polar solvent; providing metal and/or metal oxide powder; and thermally spraying the crystalline graphene oxide flakes together with the metal and/or metal oxide material on the surface, whereby the resulting composite has enhance mechanical and corrosion resistant properties.
 12. The method of claim 11, wherein the crystalline graphene/graphene oxide flakes and the metal and/or metal oxide material are dry mixed together prior to spraying.
 13. The method of claim 11, wherein the metal and/or metal oxide powder is Ni/Al₂O₃ powder.
 14. The method of claim 11, wherein the crystalline graphene/graphene oxide flakes are introduced as an atomization of a suspension separately from the metallic powder.
 15. The method of claim 14, wherein the crystalline graphene/graphene oxide flakes are suspended in water are from 0.1% to 0.5% wt to volume.
 16. The method of claim 15, wherein the concentration of crystalline graphene/graphene oxide flakes in the suspension is from 0.1% to 0.5% wt to volume in a polar solvent.
 17. The method of claim 16, wherein the crystalline graphene/graphene oxide flakes has an oxidation level >1% wt.
 18. The method of claim 14, wherein the crystalline graphene/graphene oxide flakes are suspended in ethanol or another non-polar solvent.
 19. The method of claim 18, wherein the concentration of the crystalline graphene/graphene oxide flakes suspension is from 0.1% and 0.5% wt.
 20. The method of claim 18, wherein the crystalline graphene/graphene oxide flakes has an oxidation level >1% wt. 